The present invention relates to a weft insertion system for an air jet loom, and more specifically to a weft insertion system having sub-nozzles for ejecting auxiliary air jets toward a weft passage formed in the reed.
FIG. 8 shows a conventional example. In this example, a reed 4 is swingable back and forth about an axis C of a sley word shaft 1. The reed 4 has profiled reed cents 5. Each of the profiled reed dents 5 is formed with a U-shaped recess 6 opening forwardly toward a cloth fell, and the U-shaped recesses are aligned to form a weft passage 7 extending in a weft inserting direction. Sub-nozzles 9 are arranged along the weft passage 7. In each dent, an upper edge 5A bordering the recess 6 on the upper side is sloping so that a distance R1 of an outer end X of the upper edge from the axis C of the sley sword shaft 1 is smaller than a distance R2 of an inner end of the upper edge 5A. This configuration helps a weft yarn in flying properly in the weft passage. A similar weft passage is shown in a Japanese Patent Provisional Publication No. 57-143544.
However, this configuration of the weft passage is still unsatisfactory. The auxiliary air jet of each sub-nozzle bumps against the innermost edges 5B of the recesses 6, and forms an air stream carrying the weft yarn along the weft passage. In general, the weft insertion starts when the reed 4 is in a backward motion, and terminates when the reed is in a forward motion. When the reed 4 :s moving backwards away from the cloth fell, an air stream in the weft passage tends to be left behind and to separate from the weft passage. The configuration of upper edges 5A of the weft passage 7, and the auxiliary air jets of the sub-nozzles 9 both contribute to decrease of this undesired tendency, and prevention of the weft yarn from flying out of the weft passage. Therefore, the auxiliary air jets must be made stronger than the level required for carrying the weft yarn, in order to press the weft yarn in the weft passage.
FIG. 9 shows a pressure distribution in the U-shaped recess 6. Curved lines in the recess 6 are isobaric lines connecting equal air pressure points in a weft passage section which is a predetermined distance apart from one of the sub-nozzle 9. A highest pressure point HP at which the pressure is highest in the recess 6 is located at a relatively shallow position whose distance 1.sub.1 from the open end of the recess 6 is relatively short. Generally, the weft yarn flies near the highest pressure point HP. Therefore, in the weft passage of this configuration, the flight course of the weft yarn is so shallow that the weft yarn tends to deviate from the weft passage. The conventional configuration of the weft passage is, therefore, still unsatisfactory in that the tendency to derailment of a weft yarn is relatively high, and a large air consumption is entailed to prevent such derailment.